Among the most important advances in modern medical practice has been the adoption of a variety of minimally invasive procedures. Examples of such minimally invasive procedures include angioplasty, endoscopy, laparoscopy, arthroscopy and the like. Minimally invasive surgical procedures such as these can be distinguished from conventional open surgical procedures. In these minimally invasive procedures, access to a target site within the body of a patient is achieved through a relatively small incision, into which a tubular device (including a tube of a device) is inserted or introduced. The tubular device maintains the patency of the incision, while permitting access to the target site via the interior (lumen) of the device.
In order to reach the target site, the tubular devices are often required to traverse tortuous pathways having sharp bends and angles. In some instances, and particularly when traversing such tortuous pathways, the tubular devices exhibit a tendency to kink. Kinking reduces, and often collapses, the effective inner diameter of the tubular device, thereby typically rendering the tubular device unsuitable for its intended use. Once a tubular device kinks, fluid cannot pass through the lumen of its shaft, and it becomes essentially useless, e.g., preventing inflation of balloon catheters and fluid delivery in diagnostic, infusion and drainage catheters for their satisfactory use. As a result, the initially introduced tubular device must be removed, and another tubular device must then be introduced into the patient and once again advanced through the vascular system to the narrowed site. This wastes time and increases the potential for trauma to the patient.
The tendency of a tubular device to kink is increased when the tubular device is used to introduce an interventional device into one of the many smaller vessels that branch off from major vessels. In this event, the tubular device may have insufficient flexibility at the very point where flexibility is most desired in order to enable proper positioning of the interventional device. In order to traverse the narrow confines of, e.g., the vascular system, the tubular device is typically formed of thin-wall construction. However, thin walled tubular devices often have difficulty tracking narrow vessels, and exhibit an increased propensity to kink. Increasing the thickness of the sheath tube can minimally improve the level of kink resistance, as well as the trackability of the tubular device, but limits the ability of the sheath to enter a narrow vessel, and reduces the diameter of the lumen when compared to the lumen of an otherwise similar thin-walled sheath.
To inhibit kinking, some tubular devices include a coil embedded in the wall of the catheter shaft, while other tubular devices include both a coil and a braid to take advantage of these features. One such device is found in U.S. Pat. No. 6,939,337, assigned to the assignee herein, which discloses a tubular medical device that includes a coil, such as a flat wire coil, in a stressed radially expanded condition, and a braid that extends over at least part of the coil. A bonding layer, formed from a polymer such as nylon or polyurethane, is positioned over and contacts the coil, or both the coil and the braid. The polymeric bonding layer maintains the coil in the stressed radially expanded condition, and is bonded to an inner liner, such as PTFE. By providing both a coil and a braid, the tubular device achieves some advantages attainable from each of these reinforcements. For example, the coil enables the device to better resist collapse, necking and kinking during use. The braid provides the device with enhanced pushability, trackability and torqueability. The '337 patent is incorporated by reference herein in its entirety.
Although the device of the '337 patent represents an improvement over prior art devices, it is desired to make still further improvements to such tubular devices to enhance their utility to an even greater degree than presently available. For example, FIG. 1 is a partial longitudinal sectional view of a wall 10 of a prior art tubular medical device 11 having outer and inner layers 12, 13 directly bonded to one another between spacings 14 of the windings of a coil 15 so that the two layers cannot axially move independently of each other. Because of a lack of independent movement, there can be a reduction in the overall bending flexibility of tubular medical device. Besides improving the bending flexibility of the tubular medical device, it would also be advantageous to further reduce kinkability in order for a physician to access more tortuous anatomy. Thus, it would be desirable to provide an arrangement of a coil in a tubular device that is highly resistant to kinking during use. It would also be desirable if the tubular device has a greater bending flexibility, i.e., a smaller bending radius, without kinking.